netdev - [PATCH net-next 5/6] kcm: Use sendmsg(MSG_SPLICE

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Date: Fri,  9 Jun 2023 11:02:20 +0100
From: David Howells <dhowells@...hat.com>
To: netdev@...r.kernel.org
Cc: David Howells <dhowells@...hat.com>,
	Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	David Ahern <dsahern@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Jens Axboe <axboe@...nel.dk>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Tom Herbert <tom@...bertland.com>,
	Tom Herbert <tom@...ntonium.net>
Subject: [PATCH net-next 5/6] kcm: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage

When transmitting data, call down into the transport socket using sendmsg
with MSG_SPLICE_PAGES to indicate that content should be spliced rather
than using sendpage.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: Tom Herbert <tom@...bertland.com>
cc: Tom Herbert <tom@...ntonium.net>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: Jens Axboe <axboe@...nel.dk>
cc: Matthew Wilcox <willy@...radead.org>
cc: netdev@...r.kernel.org
---
 net/kcm/kcmsock.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 7dee74430b59..3bcac1453f10 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -641,6 +641,10 @@ static int kcm_write_msgs(struct kcm_sock *kcm)
 
 		for (fragidx = 0; fragidx < skb_shinfo(skb)->nr_frags;
 		     fragidx++) {
+			struct bio_vec bvec;
+			struct msghdr msg = {
+				.msg_flags = MSG_DONTWAIT | MSG_SPLICE_PAGES,
+			};
 			skb_frag_t *frag;
 
 			frag_offset = 0;
@@ -651,11 +655,13 @@ static int kcm_write_msgs(struct kcm_sock *kcm)
 				goto out;
 			}
 
-			ret = kernel_sendpage(psock->sk->sk_socket,
-					      skb_frag_page(frag),
-					      skb_frag_off(frag) + frag_offset,
-					      skb_frag_size(frag) - frag_offset,
-					      MSG_DONTWAIT);
+			bvec_set_page(&bvec,
+				      skb_frag_page(frag),
+				      skb_frag_size(frag) - frag_offset,
+				      skb_frag_off(frag) + frag_offset);
+			iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1,
+				      bvec.bv_len);
+			ret = sock_sendmsg(psock->sk->sk_socket, &msg);
 			if (ret <= 0) {
 				if (ret == -EAGAIN) {
 					/* Save state to try again when there's